Maintaining pressure in a hydrocarbon thermalcracking zone



Oct. 24, 1967 L. F. MAYHUE MAINTAINING PRESSURE IN A HYDROCARBON THERMALCRACKING ZONE Filed Nov. 17, 1964 m v V w I; V 0') m S O .J m w l v N m 3 5| 2 I l l I I 9 so I f) f") I g f Li. 00 I LL I I J I}? I I I I I INVENTOR.

| Fv MAYHUE FEED United States Patent MAINTAINING PRESSURE IN A HYDROCARBON THERMALCRACKING ZONE Luther F. Mayhue, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware Filed Nov. 17, 1964, Ser. No. 411,856 4 Claims. (Cl. 20395) a process for cracking propane to ethylene, wherein pro- 7 pane in liquid form is heated to vapor and the vapor is passed to a cracking zone, the efliuent from the cracking zone is Water quenched, oil scrubbed, and the amount of heat supplied, and thus the amount of propane vaporized, is controlled in accordance with the pressure of the efiluent from the cracking zone. In a still further aspect, the invention relates to an apparatus for cracking hydrocarbons wherein there is provided a storage tank, a means for supplying heat to said storage tank, a thermocracking furnace, means for passing vaporized hydrocarbon from said storage tank to said cracking furnace, means for sensing the pressure of the efiluent from the cracking furnace, and means for regulating the amount of heat supplied to said storage tank in accordance'with the sensed pressure.

'In the cracking of a parafiin to an olefin in a cracking furnace, such as a Selas-type cracking furnace, carbon deposits build up in the reactor tubes. This coke deposition causes hot spots Within the tubes and impedes the flow of gases through the furnace tubes. As the cracking operation continues, and the coke depositions build up, the pressure drop across the cracking furnace increases. If the pressure of the incoming gases remains constant, the pressure of the cracked effluent will decrease. It is desirable to maintain the effluent from the cracking unit at a predetermined pressure. This pressure can be main- 1 tained, it has been discovered, by varying the input to the cracking unit in accordance with the efiluent pressure.

It is, therefore, an object of thisinvention to provide a process for cracking a hydrocarbon.

It is a further object of this invention to maintain a constant pressure in a reaction eflluent from a thermocracking furnace.

It is a still further object of this invention to minimize the effect of coke deposition in a thermocracking process.

It is a still further object of this invention to provide an apparatus for the process of this invention.

Other aspects, objects, and the several advantages of this invention are apparent from a study of this disclosure, the drawing, and the appended claims.

According to the invention, the elfluent from a thermocracking furnace is kept at a constant pressure by sensing the pressure of the eflluent and adjusting the input of the furnace accordingly. More specifically, the pressure of the efliuent is sensed and a pressure controller controls the flow of heat to a vaporizer which supplies the hydrocarbon to be cracked. j e

The invention can be better understood by reference to the accompanying drawing. The figure shows a schematic of the process of the invention.

Referring now to thedrawing, 'a liquid hydrocarbon such as liquid propane enters storage tank 2 through line 1. Heat exchanger 3 supplies heat to tank 2 sufiicient to vaporize a portion of theliquid in that tank. Heat exchanger 3 is supplied with steam from lines 4 and 5. The condensed and cooled steam leaves heat exchanger 3'through line 7. The vaporized hydrocarbon such as propane leaves tank 2 through line 9, passes through feed superheater 6 supplied with steam from line 4, which steam, after passing through feed superheater 6, is combined by way of line 8 with steam and steam condensate from line 7. Process steam is added to line 9 through line 10. The mixture of steam and propane, for example, passes into cracking furnace 11 wherein a paraffin hydrocarbon such as propane is cracked to an olefin such as ethylene. The cracking furnace can be any suitable tube type cracking furnace such as a'Selas-type cracking furnace. The eflluent from reactor 11 passing through line 12 is quenched with water from line 13. The pressure of the effluent in line 12 is sensed by pressure sensor 15 which transmits a signal to a pressure controller which in turn transmits a signal to valve 16 which operates the flow of steam through line 5 into heat exchanger 3. The 7 pressure controller maintains a predetermined pressure in efiluent line 12 and adjusts the heat supplied to heat exchanger 3 accordingly. In other words, if the pressure in the efiluent should drop due to coke deposition in the cracking furnace, pressure controller 15 will further open valve 16 to allow more.

steam to pass into heat exchanger 3. It is essential that sufficient pressure be present in the system so that there is proper operation of subsequent compression in com--- pressor 42. The increase in heat supplied to tank 2 will vaporize more hydrocarbon to pass through line 9, thus increasing the pressure of. hydrocarbon entering cracking furnace 11. The increase in pressure of hydrocarbon in line 9 will increase the pressure of effluent in line 12.

'The effiuent in line 12 is passed to carbon separator 17 wherein carbonaceous solids are removed. The vapor is contacted again with water which enters line 18 through line14. Thegravity of the effluent vapor is sensed bygravity controller 19 which adjusts a valve accordingly to allow more or less fuel to pass through line 38 into furnace 11. Theeflluent in .line 18 is contacted with oil from line 20 and the mixture .is passed to phase separator 22 wherein liquid products are separated and removed through line 26. Vaporous products leave separator 22" through line 23 and are contacted with oil from line 21.

The mixture is then separated in separator 24 and the liquid containing mostly oil and some water leaves vessel 24 through line 27 and is combined with oil and water in line 26. Heavier products are removed through separator.

28 and the resulting mixture is passed through line 29 -;into phase separator 30 wherein the heavy oil phase 31 separates from the lighter water phase 32. A small portion of the oil or oily sludge in 31 is removed from vessel 30 through line 33. The majority of the heavy aromatic oil passes out of vessel 30 through line 34- and into ,separator vessel 35 wherein a substantially pure more dense oil phase 36 is separated from a substantially pure less dense water phase 37. The oil phase 36 is removed from 35 through line 21 and recirculated to be used in the oil scrubbing part of the process. Water is removed .through line 13 and is recycled for quenching purposes. Ethylene and other gaseous hydrocarbon products leave separator 24 through line 25 by' way of a condenser in line 25 to further condense out water from the cracked vapor, and the thusly-cooled stream is charged to separator 39 to accomplish this separation. The Water stream from separator 39 is removed therefrom by line 40 and is added to .the material flowing in line 29. Cleaned product vapor is passed by line 41, compressor 42, and line 43 for further processing, including ethylene recovery, as desired.

TABLE I [Specific example, pounds/hour] Feed Efliuent Quench Water Wash Wash Liquid Liquid Vapor Stream, Component Water Wash Oil Oil Phase Phase Phase Hydrogen Methane Acetylene.-. Ethylene. Ethane Propylene Propane Butadienes Butylenes. Isobutane Pentane and Heavier Total Hydrocarbons 3, 728

Steam or Water Vapor 1 927 Liquid Water 3, 247 556 Liquid Oil 2 2,114 84, 499 86,613 Total, pounds per hour 4, 655 4, 655 3, 247 556 2, 114 84, 499 89, 899 1, 548 3, 624 Temperature, F 80 1, 500 9 90 9 90 19 100 100 1 Process steam via line (10), 390 p.s.i.a., 442 F. 2 Highly aromatic oil produced in the process; API at 60 less than 9.8.

TABLE II Unit Number Feed Feed Furnace Furnace Quenched Water Condition Vaporizer Feed Efliuent Fluid \lg iishgd Separator. Separator Separator Tcmp.,r F 80 64 282 1, 500 400 250 225 188 100 Pressure, p,s.i.a 140 114 79 2o 18 18 15 It is to be understood that the reaction generally takes sulting quenched vapors to a separator wherein oil is place :at a constant temperature. The invention provides a method for regulating the pressure of effiuent from the cracking furnace 11 while maintaining the temperature of the hydrocarbons within the cracking furnace at a constant temperature. Thus, should the temperature of hydrocarbons within furnace 11 change for any reason, such change will be reflected in the gravity of the efiluent which is sensed by gravity controller 19. Accordingly, the amount of heat supplied to furnace 11 is adjusted by adjusting the amount of fuel supplied through line 38 to a burner in the furnace.

Reasonable variation and modification in the scope of the foregoing disclosure, the drawing, and the appended claims to 'the invention, the essence of which is that the efiluent from a thermocracking reactor is maintained at a constant pressure by controlling the amount of feed supplied to thereactor in accordance with the pressure of the efiluent.

I claim:

1. A process for thermocracking of a hydrocarbon comprising fecding a liquidhydrocarbon to a storage zone, supplying heat to said storage, zone to vaporize. said hydrocarbon, passing said vaporized hydrocarbon through a cracking zone and therein cracking said hydrocarbon, removing efiluent from said cracking zone, quenching said efiluent from said crac king zone with a primary water quench, sensing the pressure are possible within the effiuent from said cracking zone, and using said sensed pressure of cffiuent in said cracking zone to adjust the supply of heat to said liquid storage zone to vaporize said hydrocarbon, separating carbonaceous solids from vapor in said effiuent, quenching the thus separated vapors with a secondary water quench, quenching said secondary water-quenched vapors with a primary oil quench, separating liquid from the oil-quenched vapors, passing said liquid thus separated from said oil-quenched vapors to a separation zone wherein water and oil are separated, quenching said oil-quenched vapors with a secondary oil quench, separating resulting quench vapors from liq uids, passing said liquids separated from said rein water, using the water from said separator as said primary and said secondary quench water, and using the, oil separated in said separator for said primary and said secondary oil quenches.

2. A process according to claim 1 wherein said hydrocarbon is propane and said cracked eflluent contains ethylene.

3. A process according property representative of the temperature of said hydrocarbon in said cracking zone is sensed after said water quenching and the heat supplied to said cracking zone: is adjusted in accordance with said sensed property to maintain the temperature of said hydrocarbon in said cracking zone at a predetermined temperature.

4. In a continuous cracking process wherein a paraffin is cracked to an olefin in a tube reactor an coke build-up in the tubes, of said reactor causes a decrease in the pressure of the efiluent from said reactor, the improvement which comprises feeding parafiinfrom a liquid storagezone from which it is vaporized, sensing the pressure of said efiluent from said reactor, and adjusting the heat supply to said liquid storage zone to vaporize said paraffin in accordance with said sensed prcssure of said reactor cfilucnt to maintain a predetermined pressure of said cfiluent.

separated fro References Cited UNITED STATESPATENTS 1,877,060 9/ 1932 Schonberg 208-106 2,236,534 4/1941 Hasche 260--683 2,671,741 3/1954 Duvall 2O848 2,769,772 11/1956 Gomory 208-430 2,906,792 9/1959 Kilpatrick 260-683 2,977,288 3/1961 Cabbage 196-132 1 3,228,858 1/1966 Matyear 196-132 DELBERT E. GANTZ, Primary Examiner.

HERBERT LEVINE, Examiner,

to claim 1 wherein an efiluent (1 wherein the 

4. IN A CONTINUOUS CRACKING PROCESS WHEREIN A PARAFFIN IS CRACKED TO AN OLEFIN IN A TUBE REACTOR AND WHEREIN THE COKE BUILD-UP IN THE TUBES OF SIA REACTOR CAUSES A DECREASE IN THE PRESSURE OF THE EFFLUENT FROM SAID REACTOR, THE IMPROVEMENT WHICH COMPRISES FEEDING PARAFFIN FROM A LIQUID STORAGE ZONE FRM WHICH IT IS VAPORIZED, SENSING THE PRESSURE OF SAID EFFLUENT FROM SAID REACTOR, AND ADJUSTING THE HEAT SUPPLY TO SAID LIQUID STORAGE ZONE TO VAPORIZE AND PARAFFIN IN ACCORDANCE WITH SAID SENSED PRESSURE OF SAID REACTOR ELLLUENT TO MAINTAIN A PREDETERMINED PRESSURE OF SAID EFFLUENT. 